Re: [OMC-Boats] 70 Seasport

On older engines, the tach is typically driven off spark pulses, picked up
at the "primary" (low voltage) side of the coil. Things to check are:

Master fuse - huge fuse in the engine bay - powers everything except
cranking and possibly tilt... Is the bilge pump/blower working? Lights?

Ignition fuse - small glass fuse behind the dashboard. Just powers the
ignition system. Labeled "IGN" on my fuse board ('70 Explorer) but might
be different in others.

Ballast resistor - not likely. If the ballast resistor was burned out -
the engine would get spark during cranking (when it is bypassed) but die
immediately afterwards. Still, use a voltmeter to check for 12V from one
side of the ballast resistor to chassis ground - it's the easiest way to
know whether any of the previously mentioned fuses are blown.

Coil - possible. I don't know a lot about coils, but I'd at least
check that the two terminals are connected - one side to 12V and the other
to the distributor. If you've got a decent multimeter, check the
resistance across it - I think it should be be a few ohms.

Distributor - also possible. Mostly just check that all the wires are
connected properly... If not, open it up and look at the points. I've
never looked at mine, so I'll leave that to one of the guys here who has
worked more on points ignition systems.

Wiring - most likely in my opinion. Look around for loose or corroded
connections. Sudden loss of spark tends to point to something falling off
- most components failures tend to be more gradual.

Good luck!

Ethan

On Mon, 5 Jul 2010, Ron Mathewson wrote:

> To the Group,
> I recently got my boat running, again after chasing down a cooling problem,
> then the fuel pump quit. I took it out yesterday, spent several hours
> running around, idle, low speed, and about 3/4 throttle with no problems.
> Today I took out again went over to a friends, docked there, where it sat
> 30-45 minutes before I went to start again. It started ran at idle, about
> 650-700 rpm, and while watching the tach i saw it drop suddenly, the motor
> sputtered and quit. I tried several times to restart with no luck. Tried a
> little gas in the carb, nothing, pulled a plug wire and saw no spark when
> placed near the block. SO at risk of sounding lazy has anyone experienced
> anything similar and if so what steps did you take to diagnose. 
> Possible a coil quit that suddenly or ballast resistor? 
>  
> Ron Mathewson
>
>
>

-- 
<a href="http://homepages.cae.wisc.edu/~brodskye/"> Ethan Brodsky </a>